添加DjongoManager后执行migrate触发django.db.utils.DatabaseError

问题概述 #

给StockInfo模型添加objects = models.DjongoManager()后，执行python3 manage.py makemigrations生成了修改StockInfo和UserProfile的id字段的迁移文件，但运行python3 manage.py migrate时失败，错误提示Djongo不支持SQL语句ALTER TABLE "dividends_info_stockinfo" ALTER COLUMN "id" TYPE int，需在不删除数据库的前提下完成迁移。

错误详情 #

cchilders@cchilders-HP-ProBook-450-G3 ~/projects/stocks_backend (save_stocks_info_to_db)$ python3 manage.py makemigrations
Migrations for 'dividends_info':
  dividends_info/migrations/0003_auto_20220814_1800.py
    - Alter field id on stockinfo
Migrations for 'users':
  users/migrations/0002_auto_20220814_1800.py
    - Alter field id on userprofile
cchilders@cchilders-HP-ProBook-450-G3 ~/projects/stocks_backend (save_stocks_info_to_db)$ python3 manage.py migrate
Operations to perform:
  Apply all migrations: admin, auth, contenttypes, dividends_info, sessions, users
Running migrations:
Not implemented alter command for SQL ALTER TABLE "dividends_info_stockinfo" ALTER COLUMN "id" TYPE int
  Applying dividends_info.0003_auto_20220814_1800...Traceback (most recent call last):
  File "/home/cchilders/.local/lib/python3.10/site-packages/djongo/cursor.py", line 51, in execute
    self.result = Query(
  File "/home/cchilders/.local/lib/python3.10/site-packages/djongo/sql2mongo/query.py", line 784, in __init__
    self._query = self.parse()
  File "/home/cchilders/.local/lib/python3.10/site-packages/djongo/sql2mongo/query.py", line 876, in parse
    raise e
  File "/home/cchilders/.local/lib/python3.10/site-packages/djongo/sql2mongo/query.py", line 857, in parse
    return handler(self, statement)
  File "/home/cchilders/.local/lib/python3.10/site-packages/djongo/sql2mongo/query.py", line 889, in _alter
    query = AlterQuery(self.db, self.connection_properties, sm, self._params)
  File "/home/cchilders/.local/lib/python3.10/site-packages/djongo/sql2mongo/query.py", line 425, in __init__
    super().__init__(*args)
  File "/home/cchilders/.local/lib/python3.10/site-packages/djongo/sql2mongo/query.py", line 84, in __init__
    super().__init__(*args)
  File "/home/cchilders/.local/lib/python3.10/site-packages/djongo/sql2mongo/query.py", line 62, in __init__
    self.parse()
  File "/home/cchilders/.local/lib/python3.10/site-packages/djongo/sql2mongo/query.py", line 441, in parse
    self._alter(statement)
  File "/home/cchilders/.local/lib/python3.10/site-packages/djongo/sql2mongo/query.py", line 500, in _alter
    raise SQLDecodeError(f'Unknown token: {tok}')
djongo.exceptions.SQLDecodeError: 

    Keyword: Unknown token: TYPE
    Sub SQL: None
    FAILED SQL: ('ALTER TABLE "dividends_info_stockinfo" ALTER COLUMN "id" TYPE int',)
    Params: ([],)
    Version: 1.3.6

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/cchilders/.local/lib/python3.10/site-packages/django/db/backends/utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
  File "/home/cchilders/.local/lib/python3.10/site-packages/djongo/cursor.py", line 59, in execute
    raise db_exe from e
djongo.database.DatabaseError

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/cchilders/projects/stocks_backend/manage.py", line 22, in <module>
    main()
  File "/home/cchilders/projects/stocks_backend/manage.py", line 18, in main
    execute_from_command_line(sys.argv)
  File "/home/cchilders/.local/lib/python3.10/site-packages/django/core/management/__init__.py", line 401, in execute_from_command_line
    utility.execute()
  File "/home/cchilders/.local/lib/python3.10/site-packages/django/core/management/__init__.py", line 395, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/home/cchilders/.local/lib/python3.10/site-packages/django/core/management/base.py", line 330, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/home/cchilders/.local/lib/python3.10/site-packages/django/core/management/base.py", line 371, in execute
    output = self.handle(*args, **options)
  File "/home/cchilders/.local/lib/python3.10/site-packages/django/core/management/base.py", line 85, in wrapped
    res = handle_func(*args, **kwargs)
  File "/home/cchilders/.local/lib/python3.10/site-packages/django/core/management/commands/migrate.py", line 243, in handle
    post_migrate_state = executor.migrate(
  File "/home/cchilders/.local/lib/python3.10/site-packages/django/db/migrations/executor.py", line 117, in migrate
    state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
  File "/home/cchilders/.local/lib/python3.10/site-packages/django/db/migrations/executor.py", line 147, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "/home/cchilders/.local/lib/python3.10/site-packages/django/db/migrations/executor.py", line 227, in apply_migration
    state = migration.apply(state, schema_editor)
  File "/home/cchilders/.local/lib/python3.10/site-packages/django/db/migrations/migration.py", line 124, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File "/home/cchilders/.local/lib/python3.10/site-packages/django/db/migrations/operations/fields.py", line 236, in database_forwards
    schema_editor.alter_field(from_model, from_field, to_field)
  File "/home/cchilders/.local/lib/python3.10/site-packages/django/db/backends/base/schema.py", line 571, in alter_field
    self._alter_field(model, old_field, new_field, old_type, new_type,
  File "/home/cchilders/.local/lib/python3.10/site-packages/django/db/backends/base/schema.py", line 721, in _alter_field
    self.execute(
  File "/home/cchilders/.local/lib/python3.10/site-packages/django/db/backends/base/schema.py", line 142, in execute
    cursor.execute(sql, params)
  File "/home/cchilders/.local/lib/python3.10/site-packages/django/db/backends/utils.py", line 98, in execute
    return super().execute(sql, params)
  File "/home/cchilders/.local/lib/python3.10/site-packages/django/db/backends/utils.py", line 66, in execute
    return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
  File "/home/cchilders/.local/lib/python3.10/site-packages/django/db/backends/utils.py", line 75, in _execute_with_wrappers
    return executor(sql, params, many, context)
  File "/home/cchilders/.local/lib/python3.10/site-packages/django/db/backends/utils.py", line 79, in _execute
    with self.db.wrap_database_errors:
  File "/home/cchilders/.local/lib/python3.10/site-packages/django/db/utils.py", line 90, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "/home/cchilders/.local/lib/python3.10/site-packages/django/db/backends/utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
  File "/home/cchilders/.local/lib/python3.10/site-packages/djongo/cursor.py", line 59, in execute
    raise db_exe from e
django.db.utils.DatabaseError

模型代码 #

dividends_info/models.py #

from djongo import models


class Dividend(models.Model):
    date = models.CharField(max_length=40)
    amount = models.FloatField()

    class Meta:
        abstract = True


class StockInfo(models.Model):
    ticker = models.CharField(max_length=100)
    name = models.CharField(max_length=255)
    description = models.TextField()
    sector = models.CharField(max_length=100)
    dividends = models.ArrayField(model_container=Dividend)

    objects = models.DjongoManager()

users/models.py #

from djongo import models


class RecentSearch(models.Model):
    search_term = models.CharField(max_length=100)

    class Meta:
        abstract = True

class UserProfile(models.Model):
    user_id = models.CharField(max_length=255)
    searches = models.ArrayField(model_container=RecentSearch)

    objects = models.DjongoManager()

生成的迁移文件 #

dividends_info/migrations/0003_auto_20220814_1800.py #

# Generated by Django 3.1.12 on 2022-08-14 18:00

from django.db import migrations, models


class Migration(migrations.Migration):

    dependencies = [
        ('dividends_info', '0002_stockinfo_ticker'),
    ]

    operations = [
        migrations.AlterField(
            model_name='stockinfo',
            name='id',
            field=models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID'),
        ),
    ]

users/migrations/0002_auto_20220814_1800.py #

# Generated by Django 3.1.12 on 2022-08-14 18:00

from django.db import migrations, models


class Migration(migrations.Migration):

    dependencies = [
        ('users', '0001_initial'),
    ]

    operations = [
        migrations.AlterField(
            model_name='userprofile',
            name='id',
            field=models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID'),
        ),
    ]

解决方法 #

原因分析 #

添加DjongoManager后，Django误判主键字段类型需要从MongoDB原生的ObjectId改为Django默认的AutoField（整数类型），但Djongo不支持这种SQL风格的字段类型修改操作——MongoDB作为文档型数据库，无需修改字段类型即可正常使用。

方案一：伪造迁移记录（推荐） #

直接告诉Django该迁移已完成，不实际修改数据库：

• 执行命令处理dividends_info应用的迁移：

  python3 manage.py migrate --fake dividends_info 0003_auto_20220814_1800
  

• 同样处理users应用的迁移：

  python3 manage.py migrate --fake users 0002_auto_20220814_1800
  

• 验证：执行python3 manage.py showmigrations，会看到这两个迁移已标记为[X]，数据库无任何改动，模型功能正常。

方案二：修改迁移文件 #

手动移除不必要的字段修改操作：

1. 打开上述两个迁移文件，删除operations列表中的migrations.AlterField操作，将其改为空列表：

   operations = []
   

2. 执行迁移命令：

   python3 manage.py migrate
   

• 此方法会让迁移执行空操作，仅更新Django的迁移记录，同样不修改数据库。

后续注意事项 #

如果模型未显式指定主键，Djongo会自动使用MongoDB的ObjectId作为主键，添加DjongoManager无需改变主键类型。后续添加Manager时，可先执行python3 manage.py makemigrations --dry-run预览迁移内容，避免生成不必要的字段修改操作。

内容的提问来源于stack exchange，提问作者codyc4321